双指针

#include <iostream>
#include <algorithm>
using namespace std;
const int N = 110;
int a[N];
int main(){
    int n;  cin >> n;
    for(int i = 0; i < n; i ++ )    cin >> a[i];
    sort(a, a + n);
    int i = 0, j = i + 1;
    int k = 0;
    while(i < n){
        if(a[i] == a[j])    j ++ ;
        else    a[k ++ ] = a[i], i = j, j = i + 1;
    }
    cout << k << endl;
    for(int i = 0; i < k; i ++ )    cout << a[i] << ' ';
    return 0;
}